DC-link voltage compensation with fuzzy-based MMC to mitigate the low-order circulating current

Abstract

ABSTRACT In this paper, a novel fuzzy controller-based technique is used to control the harmonics of the circulating currents in Pulse width modulation (PWM) based modular multilevel converters (MMC). This technique is based on average model circuit of MMC, which recognises the cross-relation in between the sub-module and system-level elements using dependent sources. In addition to improving the damping of the system, the main superiority of this technique is that it maintains the natural balancing property of DC bus system in a PWM-based MMC by combining upper and lower arms together, instead of considering separately like in existing schemes. Fuzzy controller is most suitable controller for the decision-making. Fuzzy gives more accuracy, for the nonlinear loads or heavy industrial applications. Fuzzy controller allows the reduction of the harmonics of the circulating current in the dc-link system and works effectively during the unbalanced AC grid conditions also. Therefore, it is suitable for multi-frequency AC systems. The accuracy of the proposed method is verified using simulation results which include the arm currents, common mode (circulating) currents and DC-link voltages along with AC grid voltage and currents.